Light-induced photoreductants can be employed to excite triplet state oxygen to singlet state oxygen which can be employed in the formation of hydroperoxide sites such as those employed to functionalize the initiation of polymerization reactions. Olefinic compounds such as aliphatic dienes or cyclodienes, such as cyclopentadiene, can be photo oxidized through the selective application of singlet state oxygen to produce desired end products. A particular application of the conversion of triplet state oxygen to singlet state oxygen is in the production of rubbery polymers.
Singlet state oxygen can be reacted with unsaturated polymeric rubbers, such as diene rubber compounds, to form the corresponding hydroperoxide functionalized rubbers. The hydroperoxide functionalized sites on the rubber backbone provide reactive sites which enhance the grafting efficiency in the reaction of the rubbery polymer with monomers which form pendant groups on polymeric backbones. The grafting efficiency for a particular monomer-polymer system is thus a function of the number of peroxide groups formed on each molecule of the rubbery polymer. In homogeneous reaction modes, conversion of triplet state oxygen to singlet state oxygen is accomplished in the presence of a mixture of the rubber polymer and an oxygen containing gas such as air. All things being equal, the number of pendant groups formed on the polymer backbone increases with the efficiency of the photoreductant in exciting the triplet state oxygen to a singlet state in a dispersion of the rubber in a suitable solvent such as styrene.
Suitable photoreductant formulations for the production of hydroperoxide derivatives of rubber by the reduction of triplet state oxygen to singlet state oxygen involve the application of light energy to rubber solutions of various photosensitizing agents such as methylene blue, rose bengal, and others. These agents are dissolved in a solution of a rubbery polymer through the use of an alcohol-based solubilizer such as methanol, which enhances the solubility of the photosensitizing agent in the rubber solution. The rubbery solution containing the photosynthesizing agent is oxygenated and then subjected to irradiation with light energy to convert triplet oxygen to singlet oxygen for use in the polymerization of the rubber-containing solution.